How to judge the Quality of Jewellery • How to clean jewellery • Materials we use • Diamond Information • Pearl Information • Care for your Opal • the Opalmine and the Miner
The Opal can be called the most mysterious of all gemstones. Every opal is different and individual, one of the most spectacular precious gemstone. Nature has produced a fascinating display of all colours of the spectrum by arranging amorphous silica spheres of similar size in regular layers in an infinite variety of shades, patterns and brilliance, exposed as unique precious opal. Red is rarest and can only be produced when large sphere size is present (we are talking about sizes less than 1/1000mm).
What is Opal?
Opal = Si2.nH2O Non- Crystalline form of Hydrated
Silica and contains 4% to 9% water.
Hardness: 5.0 -6.5
a mineral of medium hardness
Specific Gravity: Very low 1.9 to 2.3
Occurring as Veins and Nodules (nobbies)
Opal derives its name from the Roman word, "Opalus," meaning 'to see a change (of colour)'. The early Greeks thought opals gave their owners the powers of foresight and prophecy. Romans adored the opal as a token of hope and purity. Eastern people regarded it as sacred and Arabs believed it fell from heaven. Historically, opal has long been associated with royalty. A beautiful opal called 'Orphanus' was set in the crown of the Holy Roman Emperor and was said to guard the regal honour. Opals are also set in the crown jewels of France. Napoleon gave Josephine a beautiful opal with brilliant red flashes called 'The burning of Troy', regarding her to be his 'Helen'. Shakespeare compared the play of colour to shifting inconstancy of the mind.
How should one choose an Opal?
Each opal is very unique
which is described as having character and therefore choice is a matter of your
personal taste. Explore the full range of shapes, colours and varieties, some of
which are seldom seen outside of Australia, and choose the one that appeals to
your own personality and style.
Opal is birthstone for June & October and presented for the 14th & 18th wedding anniversary. birthstones_&_zodiacstones_&_anniversary_stones.htm
Gemstone Healing Guide:
http://www.freespiritemporium.com/guide.html
Opal helps with stomach and
intestine problems, recall of past lives, aids inner beauty, faithfulness and
eyesight.
The value of Opal is based on the following criteria: brilliance or lustre (brightness of colour), rarity of the colour or spectral colour range, type of pattern, any unique colour pattern, face-up Display (not only showing its beauty from acute angles), character, cut, shape, size, inclusions and imperfections. In these categories opal is priced per carat weight (0.2g).
Boulder Opal is occurring in thin veins in sedimentary ironstone boulders found mainly in the arid regions of western Queensland and is unique to Australia. It is naturally bonded to its host rock, dense brown ironstone. Boulder opal may be light, dark or black. By modern designers boulder opals are used cut as well as shaped like its natural features are showing. In the last twenty years this type of opal has become extremely popular as it can display the same darkness and brilliance as a high quality black opal.
The Yowah Nut
received its name from the place where it is found and from its shape. It is a
small boulder containing most diverse kernels of opal patterns and is perhaps
the most unusual variety of boulder opal. Cut and polished, they inspire many
artists to create extraordinary jewellery.
Where the Opal is mixed through the ironstone it is called Matrix Opal. Opal can also be found as a pseudomorph replacing fossil shells, bones, or wood.
The bodymass (potch) consists of
random sphere sizes in irregular layers, and is opaque, usually white, grey,
bluish, brown or black. Precious Opal often forms as a layer on potch.
Black Opal
has a natural dark or grey Potch base
or dark body colour against which the play of colour shows up brilliantly. To
find a matching pair can be very difficult. Almost all of the world's supply of
Black Opal is Australian, mainly from Lightning Ridge NSW. Quality black opals
can fetch prices equivalent to a good diamond on a per carat basis.
Lately dark Opals were found in Mintabie S.A., similar to black opal.
Light Opal
mainly comes from Coober Pedy, Mintabie and Andamooka in South Australia. The descriptive
names "white", "milky", "grey", and "semi-black" Opal refer to the natural potch
base or body colour of the Opal.
Crystal Opal
is translucent with no opaque potch base and found at all opal fields.
Some Crystal Opals show no colour unless put on a
black background. These stones when used for jewellery are usually set enclosed
with background e.g. blackened silver or cement. This does not detract from the
price.
Jelly Opal is very transparent.
The back of Opals is not always polished and can have inclusions. This
does not effect the price.
Sometimes a cutter polishes the back to give the option of setting the stone
either way.
Opal Nomenclature and Classification
Opal is Australia's National Gemstone. Australia produces 95% of the world's
natural precious opal supply. This nomenclature encompasses all types and
varieties of opal to provide a standardisation of terminology but does not
establish any valuation methodology.
The Australian Gemstone Industry Council Inc. in collaboration with the Australian Gem Industry Association Ltd., the Gemmological Association of Australia Ltd., the Lightning Ridge Miners Association Ltd. and the Jewellers Association of Australia Ltd., has produced the following nomenclature for the classification of opal.
Opal is a gemstone consisting of hydrated amorphous silica with the chemical formula SiO2.nH2O. There are two basic forms of opal described by visual appearance.
Precious Opal - is opal which exhibits the phenomenon known as play-of-colour, produced by the diffraction of white light through a micro-structure of orderly arrayed silica spheres to produce changing spectral hues.
Common Opal and Potch - is opal which does not exhibit a play-of-colour. The distinction between common opal and potch is based on formation and structure. Potch is structurally similar to precious opal but has a disorderly arrangement of silica spheres. Common opal shows some degree of micro crystallinity.
Types of Natural
Opal
Natural opal is opal which has not been treated or enhanced in any way other
than by cutting and polishing. There are three types of natural opal, with
varieties described by the two characteristics of body tone and transparency.
Natural Opal Type 1 - is opal presented in one piece in its natural state
apart from cutting or polishing and is
of substantially homogenous chemical composition.
Natural Opal Type 2 - is opal presented in one piece where the opal is
naturally attached to the host rock in
which it was formed and the host rock is of a different
chemical composition. This opal is commonly known
as boulder opal.
Natural Opal Type 3 - is opal presented in one piece where the opal is
intimately diffused as infillings of pores
or holes or between grains of the host rock in which it was
formed. This opal is commonly known as matrix
opal.
Varieties of Natural Opal
The variety of natural opal is determined by the two characteristics of body
tone and transparency.
Body Tone
The body tone of an opal is different to the play-of-colour
displayed in precious opal. There are three varieties
of natural opal based on body tone. Body tone refers to the
relative darkness or lightness of the opal when
ignoring the play-of-colour.
Black Opal - is the family of opal which shows a play-of-colour
within or on a black body tone by reference
to the AGIA Body Tone Chart N1, N2, N3 and N4 when viewed
face up.
Dark Opal - is the family of opal which shows a play-of-colour
within or on a dark body tone by reference to
the AGIA Body Tone Chart N5, N6 when viewed face up.
Light Opal - is the family of opal which shows a play-of-colour
within or on a light body tone by reference to
the AGIA Body Tone chart N7, N8 or N9 when viewed face up.
The N9 category is referred to as white opal.
Opal with a distinct coloured body (such as yellow, orange,
red or brown) should be classified as black, dark
or light opal by reference to the AGIA Body Tone Chart with a
notation stating its colour hue.
Transparency
Opal shows all forms of diaphaneity and ranges from
transparent to opaque. Natural precious opal which is
transparent to semi-transparent is known as crystal opal.
Crystal opal can have either a black, dark or light
body colour tone. The term "crystal" in this context refers
to appearance not a crystalline structure.
Opal Treatments
Opal can be subjected to various types of treatment. Present CIBJO guidelines
state that any method of treatment other than standard cutting and polishing
must be disclosed and the process used specified on all invoices, advertising
and commercial documents. Types of treatments include colour enhancement,
heating, painting, dying, resins and waxes, oiling or any application of
chemicals. Opal is treated to change its natural appearance, structure or
durability. Opal is colour enhanced in opal inlay jewellery where usually a thin
solid crystal opal has black paint or glue applied or set above black painted
jewellery.
Composite natural opal consists of natural opal laminates, manually
cemented or attached to another material. The opal component is natural opal.
There are three main forms of composite opal:
Doublet Opals - are a composition of two pieces where a
slice of natural opal is cemented to a dark base
material.
Triplet Opals - are a composition of three pieces
where a thin slice of natural opal is cemented to a dark
base material and a transparent top layer, usually of quartz
or glass.
Both
doublets and triplets imitate black opals, but are a fraction of the cost.
Mosaic and Chip Opals - are a composition of small flat
or irregularly shaped pieces of natural opal
cemented as a mosaic tile on a dark base material or
encompassed in a resin.
Synthetic Opal
Synthetic Opal is material which has essentially the same chemical composition
and physical structure as natural opal but has been made by laboratory or
industrial process. Synthetic composites exist as synthetic doublets, triplets
or mosaics and must be disclosed as synthetic composites.
Imitation Opal
Imitation Opal is material which imitates the play-of-colour of natural opal,
but does not have the same physical and chemical structure or gemmological
constants as natural opal.
Australian Opal and Gem Industry Association PTY LTD
Care for your Opal:
Protect the stone from hard hits of
other Jewellery items or heavy work e.g. bricklaying – store separately. Avoid
extreme sudden temperature changes and very low humidity (desert or bank
vaults).
Never use harsh chemicals, bleach or silver-dipping solutions to clean opal
jewellery. Careful with ultrasonic cleaners and steamers! A mild soapy lukewarm
water solution and a very soft brush may be used for jewellery set with solid
opals, but never immerse doublets or triplets in water
as the glue may
deteriorate or get soaked, which could make them dull. The safest cleaning
method is to use a soft damp cloth followed by a jeweller's polishing cloth for
the metal.
Finished opals need not be oiled or
soaked in water periodically. Some people believe that oil protects the colour.
In fact oil hides cracks in a stone, but
discolours and dulls the stone over time.
If an opal does become scratched and opaque over time, the surface can usually
be re-polished by a qualified jeweller or gem cutter.
Please visit our Australian Boulder Opal webpages: from $3600 from $3600-$1700 $1700-$1400 $1400-$1200 $1200-$800 $800-$550 $550-240 $600-$20 Australian Matrix Opals • the opalmine & the miner
Australian Opals new